1. Field of the Invention
The present invention generally relates to providing voltage isolation between separate systems in an electrical rotating apparatus. The present invention more particularly relates to providing voltage isolation between a power system and a control system in an electrical rotating apparatus.
2. Background Information
It has been known to provide voltage isolation between different electrical systems in an electrical apparatus in a variety of ways.
Voltage isolation is particularly necessary in situations where an excessive transient current or voltage in a power system can damage sensitive electrical equipment such as semiconductor devices in a control system. A conventional system can provide voltage isolation by using first and second photoisolator chips each separately coupled to a transducer for converting and transmitting a signal between separate electrical systems in an electrical apparatus. Such voltage isolation specifically utilizes an LED phototransistor device for converting an electrical signal into light in a first system; transmitting the converted signal to a second system; and, converting the light signal into an electrical signal in the second system to provide voltage isolation between the separate electrical systems. However, such photoisolator chips are generally only useful for about a 1000 v to 2000 v potential difference between systems for which voltage isolation is desired. This conventional method for providing voltage isolation is typically employed in conjunction with excitation systems such as those employed in motor drives, for example, and may employ voltage-controlled oscillators in providing voltage isolation.
Traditional voltage isolation systems and methods can also result in signal attenuation or otherwise adversely affect the integrity of the transmitted signal by changing phase, amplitude and frequency characteristics among others.
Therefore, there is an unsatisfied need in the art for a system and method that can effectively isolate voltage between independent electrical systems while maintaining the integrity of signals converted and transmitted between the independent systems in an electrical apparatus.
The fiber optic voltage isolated system of the present invention has met the above-mentioned needs. The present invention is employed in a rotating electrical apparatus that includes a power system having an input voltage and a control system that uses a signal representative of and corresponding to the input voltage.
The present invention provides a system for generating a control voltage in a low voltage control system that is representative of the input voltage in an associated high voltage power system. The system includes an oscillating device for converting the input voltage into a first frequency signal corresponding to the input voltage. This first frequency signal has a frequency which is preferably linearly proportional to the input voltage of the power system. The oscillating means is preferably a voltage-controlled oscillating means.
In the associated power system, a fiber optic transmission device is connected to the oscillating device for converting the first frequency signal into a light signal. A fiber optic cable device is provided to transmit the light signal from the power system to the control system. A fiber optic receiving means is connected to the fiber optic cable device and converts the light signal into a second frequency signal. A reconstruction apparatus is also provided for receiving the second frequency signal and reconstructing a control voltage in the control system representative of the input voltage in the power system.
The reconstruction means in the present invention can also include a counting means coupled to the fiber optic receiving means for providing an indication of the frequency of the second frequency signal. A processor or microprocessor can also be coupled to the counting means to reconstruct the control voltage by sampling the counting means at fixed time intervals.
A method associated with the isolation system of the present invention is also provided.
It is therefore an object of the present invention to provide voltage isolation between a power system and a control system in a rotating electrical apparatus.
It is a further object of the present invention to resist loss of signal integrity between a power system and a control system by employing a fiber optic cable means for transmitting a signal from a power system to a control system.
It is a further object of the present invention to reduce the harmonic content of a signal transmitted between electrically isolated systems.
These and other objects of the present invention will be more fully understood from the following description of the invention and by reference to the figures and claims appended hereto.